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        <td><h2><font color="#ffffff">Search Algorithms: PC-MB</font></h2></td>
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<p><font color="#000000">The PC-MB search is designed to search for Markov blanket DAGs of
    target variables in datasets, under the assumptions of the PC algorithm--i.e., that the true causal graph over the
    variables in the dataset does not contain any cycles, that there are no hidden common causes between variables in
    the dataset, and that no relationship between variables in the dataset is deterministic. The Markov blanket of a
    variable t is the smallest set S of variables out of a set of variables V such that t _||_ y | S for every y in V \
    (S U {t}). The Markov blanket DAG of t is the restriction of the entire causal graph over V to the variables in {t}
    U S. </font></p>
<p>MBF operates by asking a conditional independence oracle to make judgements about the independence of pairs of
    variables (e.g., X, Z) conditional on sets of variables (e.g., {Y}). Conditional indepedence tests are available for
    datasets that consist either entirely of continuous variables or entirely of discrete variables; hence, datasets of
    these types can be used as input to the algorithm. (As a way of getting one's head around how the algorithm should
    behave in the ideal, when independence tests always give correct answers, one may also use a DAG as an input to the
    algorithm, in which case graphical m-separation will be substituted for an actual independence test.) </p>
<p>In the case where a continuous dataset is used as input, the available conditional independence tests assume that the
    direct causal influence of any variable on any other is linear and that the distribution of each variable is
    Normal. </p>
<p><font color="#000000">Some of the above assumptions are not testable using observational data. They should come
    from prior knowledge or partial experiments.</font></p>
<p>Like PC, MBF returns a <em>CPDAG</em>, in this case containing: </p>
<p>(a) The target T, the true parents and children of T, and the true parents of the children of T.</p>
<p>(b) All edges among T, true parents of T, true children of T, and true parents of children of T. Some of these edges
    may not be oriented as --&gt;.</p>
<p>(c) Possibly some extra nodes and edges to account for the possibility that if some edges T---v were actually
    oriented as T--&gt;v, these nodes and adjacencies would be required in the MB DAG of T.</p>
<p>(d) No nodes or adjacencies or --&gt; edges that do no belong in some MB DAG consistent with independence facts
    supplied by (2).</p>
<p>There may also be some bidirected &lt;-&gt; edges in G_out if the independence information from (2), above, is
    inconsistent. These &lt;-&gt; edges may either be left in the final graph or oriented as if they were directed
    edges.</p>
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